Of all things to complain about, you choose Paladins using Stoneskin on themselves? Stoneskin is a flat 10% mitigation no matter who casts since now WHMs no longer have the trait that made it 18%. If a Paladin wants to use Stoneskin on themselves, let them. At least they give a damn about prevention and mitigation instead of being a typical "ignore defensive CDs" tank that we always complain about here.